The present invention relates to batteries. More particularly, it relates to organosilicon electrolytes used in combination with lithium anode/carbon monofluoride cathode batteries in structures where the battery is operable at highly elevated temperatures.
In developing optimal batteries one needs to take into account a variety of considerations. Typically, one will want to provide high voltage, store substantial amounts of energy, operate reliably and safely, provide energy on a timely response basis, keep the cost of the battery materials within commercially practical limits, provide a battery that operates long term without significant maintenance issues, and also keep the weight of the battery low.
A particularly promising type of battery for many applications is one where the anode is a lithium metal anode and the cathode is primarily made of carbon monofluoride. “Carbon monofluoride”, which is often abbreviated as “CFx”, is typically formed by a carbon substrate (such as graphite powder) having been exposed to fluorine gas at high temperature. This creates a material where fluorine is intermixed with carbon at a molar ratio near 1 to 1, but usually not exactly at 1 to 1. These materials often range from CF0.68 to CF1.12, yet still are collectively referred to as “monofluoride”. That nomenclature will be used herein as well.
FIG. 1 depicts a prior art type of battery, of the coin cell/button type. It has a disk form cathode 12, an anode 13, a metal current collector 14 attached along a side of the cathode 12, and a separator 15 impregnated with (and adjacent) electrolyte 16. There may also be metal spacers 17, a spring 18, a gasket 19, and outer casings 20 and 21. For example, the separator could be polyethylene impregnated with a mixture of polypropylene carbonate, 1,2 dimethoxyethane, and lithium tetrafluoroborate salt.
While this type of prior art device is useful for a variety of applications, it is not well suited for long term use at temperatures above 100° C. This is significant as there are various industrial and military applications for batteries which would benefit if the batteries were operable at higher temperatures (without significantly compromising other performance characteristics).
For example, in a number of oil drilling applications various battery powered devices (e.g. cameras; sensors) are used at or near the bottom of the drilled area. This can expose the device to geothermal heating extremes.
As another example, in a battlefield environment military devices can become exposed to heat generated by explosions. It is desirable for those devices (e.g. their power sources) to have improved survivability in the face of such heat exposure.
The literature has described a variety of organosilicon based electrolytes and methods for producing them. This has in some cases included a discussion of mixing those electrolytes with lithium salts for improved performance. See e.g.:
(a) 1S1M3: Me3Si—CH2O—(CH2CH2O)3-Me: K. Amine et al., Novel Silane Compounds As Electrolyte Solvents For Li-Ion Batteries, 8 Electrochemistry Communications 429-433 (2006); N. Rossi et al., Improving Properties Of Silicon-Containing Oligo(ethylene oxide) Electrolytes With Cyclic Carbonate Additives, 92 PMSE Preprints 426-427 (2005).
(b) 1NM3: Me3Si—O—(CH2CH2O)3-Me: Z. Zhang et al., Highly Conductive Oligoethyleneoxy-Functionalized Silanes, 46 Polym. Prepar. 662-663 (2005).
(c) 2NM23: Me3Si—O—(CH2CH2O)3—SiMe3: V. Phung et al., Synthesis Of Inorganic Squid Type Molecules, 472 Zeitschrift Fuer Anorganische Und Allgemeine Chemie 75-82 (1981); L. Zhang et al., Highly Conductive Trimethylsilyl Oligo(ethylene oxide) Electrolytes For Energy Storage Applications, 18 Journal Of Materials Chemistry 3713-3717 (2008).
(d) 2NM24: Me3Si—O—(CH2CH2O)4—SiMe3: V. Phung et al., and L. Zhang et al., supra.
(e) 1ND3: Me—O—(CH2CH2O)3—Si—O—(CH2CH2O)3-Me: K. Amine et al. and N. Rossi et al., supra, as well as B. Leska et al., Generation And Stability Of N-phenacyl-4-R-pyridinium Ylides In Silicon Polypodands, 700 Pol. Journal Of Molecular Structure 169-173 (2004).
(f) 1ND4: Me—O—(CH2CH2O)4—Si—O—(CH2CH2O)4-Me: K. Amine et al., N. Rossi et al., and B. Leska et al., supra.
(g) 2ND3 Me-O—(CH2CH2O)3—Si (CH3)2—O—Si (CH3)2—(CH2CH2O)3-Me: H. Nakahara et al., Passive Film Formation On A Graphite Electrode Effect Of Siloxane Structures, 160 Journal Of Power Sources 548-557 (2006); Z. Zhang et al., Oligo(ethylene glycol)-functionalized Disiloxane: Synthesis And Conductivity, 92 PMSE Preprints 365-366 (2005); and U.S. patent application publication 2007/065728.
However, to date, we are unaware of any prior suggestion to use such organosilicon based electrolytes in carbon monofluoride/lithium type batteries, much less what the attributes of such organosilicons should preferably be for such purposes, or other modifications to the batteries to enable high temperature operation.
In unrelated work there has been discussion of the use of ceramics such as alumina in separator materials in a battery system, albeit there have been indications of expected difficulties in using that material at various temperatures. See e.g. U.S. Pat. No. 3,773,558.
Hence, there is a need for improved lithium/carbon monofluoride batteries, particularly with respect to capabilities for high temperature operation.